Machines doing things on their own. Doesn't even have to be anything bad or sinister - the worst I ever had it in real life was back when I worked as a projectionist/AV operator at my university, and this old 16mm kept playing after I shut it off. The reason turned out to be something stupid (I forget what), but it freaked me the hell out. TV glowing after you turn it off? Creepy. Elevator showing up and opening for you with nobody in it, before you've hit the button? Freaking terrifying.

I'm sure the X-Files is somehow to blame for all this, but I can't remember how.